Hi Dave
Seems a very long time that for that resollution , How long is the move ?., also not sure if it makes a diffenece but what is your Broadband speed ?.
As Martins link above.
But generaly if you load the film into the moviemaker and then save it as a new avi file it will make it smaller by default.
Also Depending on your account you may be able to have longer than 10 minutes.